Publications by authors named "Thomas Strasser"

17 Publications

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Correction to: Temporary materials: comparison of in vivo and in vitro performance.

Clin Oral Investig 2021 Jul 21. Epub 2021 Jul 21.

Department of Prosthetic Dentistry, Regensburg University Medical Center, D-93042, Regensburg, Germany.

A Correction to this paper has been published: https://doi.org/10.1007/s00784-021-04067-4.
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http://dx.doi.org/10.1007/s00784-021-04067-4DOI Listing
July 2021

Long-term clinical performance and complications of zirconia-based tooth- and implant-supported fixed prosthodontic restorations: A summary of systematic reviews.

J Dent 2021 Jun 11;111:103723. Epub 2021 Jun 11.

Department of Prosthetic Dentistry, UKR University Hospital Regensburg, 93042 Regensburg, Germany. Electronic address:

Objectives: To present an overview on systematic reviews on prosthodontic zirconia restorations and to discuss long-term complications as well as information on anatomical and functional changes to the masticatory system.

Data/sources: MEDLINE, EMBASE, Trip medical, and Cochrane Library databases were searched for systematic reviews up to February 2021. Bias was assessed and clinical survival and complications were analyzed.

Study Selection: 38 eligible articles published between 2006 and 2021 were included. The reviews were based on 128 in vivo studies on approximately 10,000 zirconia restorations. 5-year cumulative survival rates varied between 91.2% and 95.9% for tooth-supported (TS) single crowns (SC), 89.4% and 100% for TS multi-unit fixed dental prostheses (FDP), 97.1% and 97.6% for implant-supported (IS) SCs and 93.0% and 100% for IS FDPs. Chipping was the most often technical complication, followed by framework fracture, loss of retention, marginal discrepancies/discoloration, occlusal roughness and abutment/screw loosening. Color mismatch was the only esthetic complication. Biological complications were caries, endodontic complications, tooth fracture, periodontal disease, abrasion/attrition, persisting pain, high sensitivity, peri‑implantitis and soft tissue issues. Patients with bruxism were only examined sporadically.

Conclusions: 5-year results for zirconia restorations were satisfactory. The predominant technical problem of veneering fractures could be overcome with adapted design or fabrication and application of monolithic restorations, but reviews of clinical studies on this subject are rare. The impact of zirconia restorations on the masticatory system remains unclear.

Clinical Significance: Zirconia restorations are experiencing a rapidly increasing use in dental practice. Being highly wear-resistant, hard and durable, it can be assumed that they do not follow natural abrasion and changes in the masticatory system. Possible long-term effects on the stomatognathic system as a whole should therefore be considered.
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http://dx.doi.org/10.1016/j.jdent.2021.103723DOI Listing
June 2021

Machine-driven simulation of removing luting agent remnants from implant surfaces: An investigator-independent assessment of cleaning protocols.

J Mech Behav Biomed Mater 2021 09 25;121:104584. Epub 2021 May 25.

Department of Prosthodontics, University Hospital Regensburg, Germany.

Introduction: To simulate removing luting agent remnants from crowns fixed onto implant-abutment analogs using a standardized machine-driven protocol including a scaler and air polishing or sonic.

Material And Methods: A motor-driven device was constructed that controlled the rotational speed of the specimens, machining distance, contact pressure, and working time. A standardized layer of cement (Provicol, VOCO; Cuxhaven, G; Ketac Cem, 3MEspe; Seefeld, G; or Rely X Unicem, 3MEspe, Seefeld, G) was placed onto the finishing line of the crowns luted onto titanium-abutment analogs. The cement layer was scaled with a fresh titanium scaler maneuvered by the motor-driven device and treated with air polishing or sonic. Protocol 1: Scaling only for 20s, 40s, or 60s; n=20; protocol 2: 40s of scaling plus 20s of air polishing; protocol 3: 20s of scaling plus 40s of air polishing; protocol 4: 20s of scaling plus 40s of sonic; protocol 5: 40s of scaling plus 20s of sonic; protocols 2-5: n=10. Cement remnants were counted digitally as "percentage of remnants".

Statistics: mean, standard deviation, Bonferroni post hoc tests; α=0.05.

Results: Ketac Cem was easily removed by scaling only and Provicol by scaling and air polishing, but the self-adhesive resin composite cement Rely X Unicem was not removable with the device. Only remnants of Provicol could be significantly reduced by further treatment after scaling (p<0.001).

Conclusion: The presented motor-driven device enables reproducible investigations of various cleaning protocols and is thus useful to create an overview of cleaning protocols needed for the different types of cement.
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http://dx.doi.org/10.1016/j.jmbbm.2021.104584DOI Listing
September 2021

Pilot in-vitro study on insertion/removal performance of hand-cast, milled and 3D printed splints.

J Mech Behav Biomed Mater 2021 09 27;121:104612. Epub 2021 May 27.

Department of Prosthetic Dentistry, UKR University Hospital Regensburg, 93042, Regensburg, Germany. Electronic address:

Objectives: The aim of this in-vitro pilot study was to establish a splint testing method and compare insertion/removal performance of dental splints.

Materials And Methods: 56 identical lower jaw splints (n = 8 per group) were manufactured from 2x methacrylate (MA) hand-cast (reference material), deep-drawn Polyethyleneterephthalate, combined deep-draw MA hand-cast, 2x CAD/CAM-milled MA and 3D-printed MA systems. After 10 days water storage (37 °C), cyclic pull-off and insertion performance on a metal jaw was investigated. Statistics; Shapiro-Wilk-test, one-way-ANOVA; post-hoc-Bonferroni, Kaplan-Meier-survival, α = 0.05.

Results: Mean insertion/pull-off cycles varied significantly (p = 0.000) between 864 cycles (MA) and 202640 cycles (Deep Draw MA). Fracture of the splints was characterized by brittle individual fractures in the 31-34 region and most fractures in region 35 (44 of 56 splints). Finite element analysis confirmed the type and location of failure.

Conclusions: Deep-draw, cast methacrylate and combined systems showed longer insertion/pull-off system cycles in comparison to printed or milled splints. Insertion/pull-off performance showed differences between the tested splint systems and indicates the influence of the processing.

Clinical Relevance: The presented in-vitro test allowed for estimating the clinical insertion/pull-off performance of dental splints.
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http://dx.doi.org/10.1016/j.jmbbm.2021.104612DOI Listing
September 2021

Finite element analysis of occlusal interferences in dental prosthetics caused by occlusal adjustment.

Int J Prosthodont 2021 Feb 23. Epub 2021 Feb 23.

Purpose: To investigate the influence of occlusal interference in dental prosthetics using finite element analysis (FEA).

Materials And Methods: The FEA model designed for this study centered on an all-ceramic, bi-layered, fixed partial denture (FPD) retained on the maxillary first premolar and molar, with the second premolar replaced by a pontic. The surrounding structures, such as the neighboring teeth, antagonists, and periodontium, were modeled. Four different load cases were designed at occlusal interferences of 0, 8, 12, and 24 μm, loaded by a simulated bite force of 300 N. Principal and von Mise stresses, as well as strain, were evaluated for all included structures.

Results: For interferences of 12 and 24 μm, failure-relevant tensile stresses in the veneering layer were observed at the occlusal surfaces. Stress found in the zirconia FPD did not reach fatigue or flexural strength for any test load.

Conclusion: Peak tensile stress was observed in close proximity to occlusal contact points, increasing with increasing occlusal interference. The FEA results suggested that the majority of occlusal stress is absorbed by the deformation of the periodontal ligament. Framework failure caused by the simulated interferences was not expected. Surface defects may ultimately lead to failure due to fracture or chipping, especially in cases of weaker ceramics or veneering.
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http://dx.doi.org/10.11607/ijp.7178DOI Listing
February 2021

Multilayer zirconia: Influence of positioning within blank and sintering conditions on the in vitro performance of 3-unit fixed partial dentures.

J Prosthet Dent 2020 Dec 30. Epub 2020 Dec 30.

Researcher, Department of Prosthetic Dentistry, UKR University Hospital Regensburg, Regensburg, Germany.

Statement Of Problem: Multilayer zirconia blanks comprise material layers with different optical and mechanical properties. Whether positioning within the blank, as well as variation in the sintering procedure, will lead to restorations with different properties is unclear.

Purpose: The purpose of this in vitro study was to test the influence of sintering procedures and positioning in a multilayer blank on the in vitro performance of 3-unit zirconia fixed partial dentures.

Material And Methods: Human molars were embedded in acrylic resin and prepared for 3-unit fixed partial dentures. Anatomic contour prostheses were milled from zirconia blanks (ZirCAD Prime 16 mm) in 3 different positions: above (cusp-top at the top of the blank), central (center of the prosthesis in the center of the blank), and bottom (margins at the lower edge of the blank). Sintering time (2:26, 4:25, 9:50 hours:minutes) was varied for the central and bottom prostheses. All prostheses were glazed and adhesively bonded. Thermocycling and mechanical loading was performed at 2×3000×5 °C/55 °C in distilled water for 1.2×10 cycles at a 50-N load. Then, fracture force was determined with a universal testing device by using central loading, a Ø12-mm steel ball, a 1-mm tin foil, and a rate of 1 mm/min. Failure was defined as 10% force drop or acoustic signal (crack). Statistical analysis was performed with 1-way ANOVA and Bonferroni correction (α=.05).

Results: All fixed partial dentures survived thermocycling and mechanical loading. Fracture forces varied between 1002 ±446 N (above; 9:50 hours) and 1760 ±607 N (central; 9:50 hours). The 1-way ANOVA revealed no statistically significant differences (P=.059) among the groups. Individual significant differences (P=.048) were found between prostheses from positions above, 9:50 hours, and central, 9:50 hours. For normal and long sintering times, fracture forces were highest in the central position.

Conclusions: The sintering process and positioning of restorations within a multilayer zirconia blank have little effect on the mechanical properties of the prostheses.
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http://dx.doi.org/10.1016/j.prosdent.2020.11.009DOI Listing
December 2020

In vitro performance and fracture resistance of interim conventional or CAD-CAM implant-supported screw- or cement-retained anterior fixed partial dentures.

J Prosthet Dent 2020 Sep 19. Epub 2020 Sep 19.

Professor and Engineer, Department of Prosthetic Dentistry, UKR University Hospital Regensburg, Regensburg, Germany.

Statement Of Problem: Interim restorations represent an essential clinical treatment step; however, limited information is available concerning the performance of computer-aided design and computer-aided manufacturing (CAD-CAM) interim materials.

Purpose: The purpose of this in vitro study was to evaluate the performance and fracture load of resin anterior implant-supported interim fixed partial dentures (IFPDs).

Material And Methods: Identical anterior resin IFPDs (maxillary central incisor to canine; n=16 per material) were milled from polymethylmethacrylate (PMMA) or di-methacrylate (DMA) systems with different filler content. The IFPD groups were split to simulate a chairside (cemented implant-supported prosthesis) or laboratory procedure (screw-retained implant-supported prosthesis). A cartridge DMA material served as a control. After interim cementation, combined thermocycling and mechanical loading (TCML) was performed on all restorations to approximate a maximum of 2.5 years of clinical function. Behavior during TCML and fracture force was determined, and failures were analyzed. The data were statistically investigated (Kolmogorov-Smirnov test, 1-way-ANOVA; post hoc Bonferroni, Kaplan-Meier survival, α=.05).

Results: Drop out during TCML varied between no failures and complete failure during loading. For most systems, failure occurred between 120 000 and 600 000 mechanical loading cycles. For IFPDs without a screw channel fracture, values varied between 644 ±263 N and 987 ±101 N. Those with a screw channel fracture failed between 493 ±89 N and 951 ±248 N. Individual IFPDs had significantly higher mean fracture loads (P<.002), but the mean fracture values between IFPDs with and without a screw channel were not significantly different (P>.137). Failures were characterized by fracture of the connector (n=53) followed by mixed failures (n=22) or fractures at the abutment (n=21).

Conclusions: These interim materials are sufficiently fracture resistant for the fabrication of implant-supported anterior IFPDs and are expected to survive between 6 months and 2 years before failure. The stability of IFPDs depended on the type of material but not on the restoration design (with or without a screw channel).
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http://dx.doi.org/10.1016/j.prosdent.2020.08.008DOI Listing
September 2020

Fatigue and wear behaviour of zirconia materials.

J Mech Behav Biomed Mater 2020 10 9;110:103970. Epub 2020 Jul 9.

DDS, Department of Prosthetic Dentistry, UKR University Hospital Regensburg, 93042, Regensburg, Germany.

Objectives: Comparison of in-vitro fatigue and wear performance of 3Y-, 4Y-, 5Y-TZP and lithiumdisilicate ceramic, multilayer/monolayer 4Y-TZP and variation of wall thickness at 5Y-TZP.

Method And Materials: Crowns (n = 96; 6 groups à 16) were made of 3Y-TZP-LA, 4Y-TZP (multilayer and monolayer), 5Y-TZP (0,5mm/1 mm wall thickness) and lithiumdisilicate. 8 per group were stored in water (24hrs), 8 underwent TCML (1.200.000 × 50N; 2x3000x5°/55 °C; HO, 2min cycle). Fracture force was determined by static loading (v = 1 mm/min, steel sphere with tin foil, diameter = 12 mm). Pin-on-block wear test was performed (steatite antagonist d = 3 mm; 50N, 120,000 cycles, 1.2Hz, lateral motion: 1 mm, antagonist lift: 1 mm, n = 8). Roughness, wear depth [μm] and antagonist wear were determined (3-D-laser-microscope, KJ3D, Keyence, J).

Statistics: one-way-ANOVA; Bonferroni-post-hoc-test; α = 0.05.

Results: Fracture forces varied between 1211N (5Y,TCML) and 3952N (4Y-Mult,TCML). Individual significant differences (p ≤ 0.025) were found between materials. Increase of wall thickness (5Y; 0.5 mm/1.0 mm) lead to a non-significant (p ≥ 0.442) increase of fracture force. 4Y and 4Y-multilayer zirconia showed no significantly different (p ≥ 0.073) fracture forces. Zirconia mean wear (3Y:10.0 ± 3.9 μm, 4Y:19.8 ± 3.8 μm, 5Y:10.9 ± 6.8 μm) was not significantly (p = 1.000) different. Lithiumdisilicate ceramic (149.3 ± 45.4 μm) and human enamel (434.2 ± 131.3 μm) provided significantly (p ≤ 0.002) higher wear. Antagonistic wear against lithiumdisilicate (17.5 ± 3.9%) and human enamel (6.7 ± 3.0%) was significantly (p ≤ 0.007) lower than against zirconia (4Y:31.9 ± 8.0% - 5Y:27.6 ± 5.8%).

Conclusion: Fracture force of 5Y-TZP differs from 4- or 3-Y-TZP. Mechanical characteristics and dimensional requirement of 5Y-TZP are comparable to lithiumdisilicate. Mono- or multilayer 4Y-TZP provided comparable fracture forces. Wear was comparable between zirconia systems and lower in comparison to lithiumdisilicate or enamel.
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http://dx.doi.org/10.1016/j.jmbbm.2020.103970DOI Listing
October 2020

Temporary materials: comparison of in vivo and in vitro performance.

Clin Oral Investig 2020 Nov 24;24(11):4061-4068. Epub 2020 Jun 24.

Department of Prosthetic Dentistry, Regensburg University Medical Center, D-93042, Regensburg, Germany.

Objective: The aim of this investigation was to compare clinical performance and in vitro wear of temporary CAD/CAM and cartridge crowns. This study is an approach to estimate the influence of in vivo use and laboratory simulation on temporary crowns.

Materials And Methods: A total of 90 crowns were fabricated from each temporary CAD/CAM or cartridge material. Also, 10 crowns of each material were clinically applied for 14 days, and 80 identical duplicate restorations were investigated in the laboratory after storage in water (14 days; 37 °C) and subsequent thermal cycling and mechanical loading (TCML, 240.000 × 50N ML, 600 × 5°C/55 °C). After in vivo application or in vitro aging, facture force, superficial wear (mean and maximum), surface roughness (Ra, Rz), thermal weight loss (TGA), and heat of reaction (DSC) were determined for all crowns.

Statistics: Bonferroni post hoc test; one-way analysis of variance (ANOVA); α = 0.05).

Results: The fracture resistance of the temporary materials varied between 1196.4 (CAD in vivo) and 1598.3 N (cartridge crown in vitro). Mean (maximum) wear data between 204.7 (386.7 μm; cartridge in vitro) and 353.0 μm (621.8 μm; CAD in vitro) were found. Ra values ranged between 4.4 and 4.9 μm and Rz values between 36.0 and 40.8 μm. DSC and TG analysis revealed small differences between the materials but a strong influence of the aging process.

Conclusions: Comparison of in vivo and in vitro aging led to no significant differences in fracture force and wear but differences in roughness, DSC, and TGA. SEM evaluation confirmed comparability. Comparison of CAD/CAM and cartridge temporary materials partially showed significant differences.

Clinical Relevance: In vitro aging methods might be helpful to estimate materials' properties before principal clinical application. CAD/CAM and cartridge temporary materials provided comparable good clinical performance.
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http://dx.doi.org/10.1007/s00784-020-03278-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8275555PMC
November 2020

Laboratory performance and fracture resistance of CAD/CAM implant-supported tooth-coloured anterior FDPs.

J Dent 2020 05 20;96:103326. Epub 2020 Mar 20.

Department of Prosthetic Dentistry, UKR University Hospital Regensburg, 93042, Regensburg, Germany.

Objectives: This study investigated the in-vitro performance and fracture force of anterior implant-supported tooth-coloured fixed dental prosthesis (FDPs). Different material types with varying flexural strength and modulus of elasticity were compared with screw-retained or bonded application.

Materials And Methods: Identical anterior FDPs (tooth 11-13; n = 80) from materials (flexural strength 240-1150 MPa, modulus 7.6-210 GPa; 1x lithiumdisilicate ceramic, 2x zirconia (4Y-TZP, 5Y-FSZ), 3x resin-based composites (with different flexural strength and modulus)) were milled. FDPs were grouped into chairside (bonded) and labside (screw-retained) procedure. To simulate a 5-year clinical application, thermal cycling with mechanical loading (TCML) was accomplished. TCML-performance and fracture force were evaluated and failure patterns were analysed. Data were statistically investigated (Kolmogorov-Smirnov-test, one-way-ANOVA; post-hoc-Bonferroni, α = 0.05).

Results: TCML did not lead to any cracks, fractures or chipping on all tested FDPs. Fracture values varied between 1208.9 ± 354.6 N (experimental resin-based composite) and 2094.3 ± 293.4 N (4Y-TZP) for FDPs without screw channel. With screw channel the results ranged between 1297.9 ± 268.3 N (5Y-FSZ) and 2129.3 ± 321.7 N (4Y-TZP). The influence of the screw channel was not significant for all materials (p ≥ 0.218). Modulus of elasticity and flexural strength had influence on the fracture force only in the individual material groups. Fractures at the connector were predominant for ceramic and zirconia. Resin-based composites primarily showed radial fractures in abutment region or mixed failure types. FDPs with/without screw-channel showed comparable types of failure.

Conclusions: TCML did not lead to drop-outs or failures for all FDPs. Individual materials showed no different in-vitro performance, but varying fracture force after TCML. Independent from material, screw channels did not weaken the FDPs. All tested systems showed sufficient properties for an anterior implant application.
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http://dx.doi.org/10.1016/j.jdent.2020.103326DOI Listing
May 2020

Fracture force of CAD/CAM resin composite crowns after in vitro aging.

Clin Oral Investig 2020 Jul 11;24(7):2395-2401. Epub 2019 Nov 11.

Department of Prosthetic Dentistry, UKR University Hospital Regensburg, 93042, Regensburg, Germany.

Objectives: The aim of this in vitro study was to investigate the influence of material, preparation, and pre-treatment on the aging and fracture force of CAD/CAM resin composite molar crowns.

Materials And Methods: CAD/CAM molar crowns (n = 80) were milled from four resin composites (Block HC, Shofu; Lava Ultimate, 3 M; Grandio Blocs, Voco; and Tetric CAD, Ivoclar Vivadent, with/without sandblasting). Extracted human teeth were prepared with optimal preparation (height 6-8 mm, angle 6-8°) or worst-case preparation (height 3.5-4 mm, angle 10-15°). Both groups were prepared with a 1-mm deep cervical circular shoulder. Crowns were adhesively bonded after corresponding tooth treatment required for the individual adhesive systems (Table 1). Specimens were aged for 90 days in water storage (37 °C) and subsequently subjected to thermal cycling and mechanical loading (TCML 3000 × 5 °C/3000 × 55 °C, 2 min each cycle, H20 distilled; 1.2 × 10 cycles à 50 N, 1.6 Hz). De-bonding and fracture force was determined.

Statistics: one-way-ANOVA; post hoc Bonferroni, α = 0.05.

Results: Four crowns of Lava Ultimate with worst-case preparation de-bonded during TCML. Individual crowns without sandblasting treatment (3x Tetric CAD with optimal preparation; 1x Tetric CAD with worst-case preparation) de-bonded during water storage. One crown of Grandio Blocs with optimal preparation showed a small chipping during TCML. All other crowns survived TCML and water storage without failure. Fracture forces differed between 1272 ± 211 N (Lava Ultimate) and 3061 ± 521 N (Tetric CAD). All Grandio Blocs and Tetric CAD crowns revealed significantly (p ≤ 0.023) higher fracture forces than Block HC or Lava Ultimate crowns. No significantly different (p > 0.05) fracture forces were found between optimal or worst-case preparation/fit groups.

Conclusions: De-bonding during water storage and TCML was dependent on material and crown pre-treatment. Therefore, surface roughening seems strongly required. Fracture forces were not influenced by preparation but by the type of material.

Clinical Relevance: Clinical success and de-bonding of CAD/CAM resin composite crowns is strongly influenced by the type of material and its pre-treatment.
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http://dx.doi.org/10.1007/s00784-019-03099-1DOI Listing
July 2020

Dynamic fatigue of composite CAD/CAM materials.

J Mech Behav Biomed Mater 2019 10 7;98:311-316. Epub 2019 Jul 7.

Department of Prosthetic Dentistry, UKR University Hospital Regensburg, 93042, Regensburg, Germany. Electronic address:

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http://dx.doi.org/10.1016/j.jmbbm.2019.07.002DOI Listing
October 2019

Roughness, surface energy, and superficial damages of CAD/CAM materials after surface treatment.

Clin Oral Investig 2018 Nov 5;22(8):2787-2797. Epub 2018 Feb 5.

Department of Prosthetic Dentistry, UKR University Hospital Regensburg, 93042, Regensburg, Germany.

Objectives: The aim of this study was to examine the effects of surface pre-treatment on CAD/CAM materials including ceramics, zirconia, resin-infiltrated ceramic, and resin-based composite.

Materials And Methods: Specimens were made of ten CAD/CAM materials (Celtra Duo, Degudent, D; Vita Suprinity, Vita, D; E.max CAD, Ivoclar-Vivadent, FL; E.max ZirCAD, Ivoclar-Vivadent, FL; Vita Enamic, Vita, D; Cerasmart, GC, B; LAVA Ultimate, 3M, D; SHOFU Block HC, SHOFU, US; Grandio Blocs, VOCO, D; BRILLIANT Crios, Coltene, CH) and pretreated to represent clinical procedures (Hf 20 s/5%; phosphoric acid 20 s/37%; Monobond etch and prime (Ivoclar-Vivadent, FL); water-cooled diamond bur (80 μm; 4 μm); AlO-blasting (50 μm/1 bar, 50 μm/2 bar, 120 μm/1 bar, 120 μm/2 bar); untreated; manufacturer's instructions). SEM-analysis (Phenom, FEI, NL) of the surfaces was performed (magnifications ≤ 10,000×). Roughness values R, R (KJ 3D, Keyence, J), and surface energy SE (OCA15 plus, SCA20, DataPhysics, D) were determined (statistics: non-parametric Mann-Whitney U test/Kruskal-Wallis test for independent specimen, α = 0.05).

Results: Kruskal-Wallis revealed significant (p < 0.001) differences for all materials with different surface treatments. Roughness ranged from R = 0.05 μm (VS; D4)/R = 0.41 μm (VS; D4) to R = 1.82 μm (EMA; SB120/2)/R = 12.05 μm (CS; SB 120/2), SE from 22.7 mN/m (VE; M) to 52.8 mN/m (CD; M). SEM analysis showed material-dependent damages after pre-treatment.

Conclusion: Different CAD/CAM materials require individual pre-treatment for optimized and protective surface activation.

Clinical Relevance: Cementation is a key factor for clinical success. Given the variety of available CAD/CAM materials, specific procedures are needed.
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http://dx.doi.org/10.1007/s00784-018-2365-6DOI Listing
November 2018

Local variance for multi-scale analysis in geomorphometry.

Geomorphology (Amst) 2011 Jul;130(3-4):162-172

Department of Geography and Geology, University of Salzburg, Hellbrunnerstraße 34, Salzburg 5020, Austria.

Increasing availability of high resolution Digital Elevation Models (DEMs) is leading to a paradigm shift regarding scale issues in geomorphometry, prompting new solutions to cope with multi-scale analysis and detection of characteristic scales. We tested the suitability of the local variance (LV) method, originally developed for image analysis, for multi-scale analysis in geomorphometry. The method consists of: 1) up-scaling land-surface parameters derived from a DEM; 2) calculating LV as the average standard deviation (SD) within a 3 × 3 moving window for each scale level; 3) calculating the rate of change of LV (ROC-LV) from one level to another, and 4) plotting values so obtained against scale levels. We interpreted peaks in the ROC-LV graphs as markers of scale levels where cells or segments match types of pattern elements characterized by (relatively) equal degrees of homogeneity. The proposed method has been applied to LiDAR DEMs in two test areas different in terms of roughness: low relief and mountainous, respectively. For each test area, scale levels for slope gradient, plan, and profile curvatures were produced at constant increments with either resampling (cell-based) or image segmentation (object-based). Visual assessment revealed homogeneous areas that convincingly associate into patterns of land-surface parameters well differentiated across scales. We found that the LV method performed better on scale levels generated through segmentation as compared to up-scaling through resampling. The results indicate that coupling multi-scale pattern analysis with delineation of morphometric primitives is possible. This approach could be further used for developing hierarchical classifications of landform elements.
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http://dx.doi.org/10.1016/j.geomorph.2011.03.011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3115023PMC
July 2011

The two origins of hemocytes in Drosophila.

Development 2003 Oct 20;130(20):4955-62. Epub 2003 Aug 20.

Institut für Allgemeine Zoologie und Genetik der Westfälischen Wilhelms-Universität, Schlossplatz 5, 48149 Münster, Germany.

As in many other organisms, the blood of Drosophila consists of several types of hemocytes, which originate from the mesoderm. By lineage analyses of transplanted cells, we specified two separate anlagen that give rise to different populations of hemocytes: embryonic hemocytes and lymph gland hemocytes. The anlage of the embryonic hemocytes is restricted to a region within the head mesoderm between 70 and 80% egg length. In contrast to all other mesodermal cells, the cells of this anlage are already determined as hemocytes at the blastoderm stage. Unexpectedly, these hemocytes do not degenerate during late larval stages, but have the capacity to persist through metamorphosis and are still detectable in the adult fly. A second anlage, which gives rise to additional hemocytes at the onset of metamorphosis, is located within the thoracic mesoderm at 50 to 53% egg length. After transplantation within this region, clones were detected in the larval lymph glands. Labeled hemocytes are released by the lymph glands not before the late third larval instar. The anlage of these lymph gland-derived hemocytes is not determined at the blastoderm stage, as indicated by the overlap of clones with other tissues. Our analyses reveal that the hemocytes of pupae and adult flies consist of a mixture of embryonic hemocytes and lymph gland-derived hemocytes, originating from two distinct anlagen that are determined at different stages of development.
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http://dx.doi.org/10.1242/dev.00702DOI Listing
October 2003

FlyMove--a new way to look at development of Drosophila.

Trends Genet 2003 Jun;19(6):310-1

Institut für Neurobiologie, Universität Münster, Badestrasse 9, D-48149 Münster, Germany.

Development of any organism requires a complex interplay of genes to orchestrate the many movements needed to build up an embryo. Previously, work on Drosophila melanogaster has provided important insights that are often applicable in other systems. But developmental processes, which take place in space and time, are difficult to convey in textbooks. Here, we introduce FlyMove (http://flymove.uni-muenster.de), a new database combining movies, animated schemata, interactive "modules" and pictures that will greatly facilitate the understanding of Drosophila development.
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http://dx.doi.org/10.1016/S0168-9525(03)00050-7DOI Listing
June 2003

The formation of syncytia within the visceral musculature of the Drosophila midgut is dependent on duf, sns and mbc.

Mech Dev 2002 Jan;110(1-2):85-96

Institut für Allgemeine Zoologie und Genetik der Westfälischen Wilhelms-Universität, Schlossplatz 5, 48149 Münster, Germany.

The visceral musculature of the Drosophila midgut consists of an inner layer of circular and an outer layer of longitudinal muscles. Here, we show that the circular muscles are organised as binucleate syncytia that persist through metamorphosis. At stage 11, prior to the onset of the fusion processes, we detected two classes of myoblasts within the visceral trunk mesoderm. One class expresses the founder-cell marker rP298-LacZ in a one- to two-cells-wide strip along the ventralmost part of the visceral mesoderm, whereas the adjacent two to three cell rows are characterised by the expression of Sticks-and-stones (SNS). During the process of cell fusion at stage 12 SNS expression decreases within the newly formed syncytia that spread out dorsally over the midgut. At both margins of the visceral band several cells remain unfused and continue to express SNS. Additional rP298-LacZ-expressing cells arise from the posterior tip of the mesoderm, migrate anteriorly and eventually fuse with the remaining SNS-expressing cells, generating the longitudinal muscles. Thus, although previous studies proposed a separate primordium for the longitudinal musculature located at the posteriormost part of the mesoderm anlage, our cell lineage analyses as well as our morphological observations reveal that a second population of cells originates from the trunk mesoderm. Mutations of genes that are involved in somatic myoblast fusion, such as sns, dumbfounded (duf) or myoblast city (mbc), also cause severe defects within the visceral musculature. The circular muscles are highly unorganised while the longitudinal muscles are almost absent. Thus the fusion process seems to be essential for a proper visceral myogenesis. Our results provide strong evidence that the founder-cell hypothesis also applies to visceral myogenesis, employing the same genetic components as are used in the somatic myoblast fusion processes.
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http://dx.doi.org/10.1016/s0925-4773(01)00567-6DOI Listing
January 2002